Since the first satellite of the global positioning system (GPS) was orbited by the Unite States Department of Defense, the GPS has become a household word in the global navigation and positioning field and the satellite measurement field. As telecommunication and information technologies develop rapidly, and more particularly, as new Internet and wireless data communication technologies emerge, positioning and measurement applications of the GPS continue to evolve from long-time static measurements to real-time dynamic positioning.
The GPS was first employed to navigate planes or ships, and has since been increasingly used in the daily life of modern people. For example, GPS in combination with an e-map can be used for navigating a vehicle, so that a driver can arrive at a destination easily. The GPS is also used for leisure activities such as hiking and mountain climbing, and accordingly a hiker and a climber can more easily find a destination or route home. In sum, capabilities of the GPS have changed the daily life of many people
However, the GPS is not able to function smoothly in all places. FIG. 1 shows a schematic diagram of an operation principle of a GPS 1. As clearly seen in FIG. 1, a mobile receiving device 10 such as a mobile phone or a personal digital assistant (PDA) receives a satellite signal 110 transmitted from a plurality of artificial satellites 11 orbiting around the earth 12. After receiving the satellite signals 110, the mobile receiving device 10 calculates a two dimensional coordinate position or a three dimensional coordinate position via triangulation. Therefore, a user obtains a current position of the user via the two or three dimensional coordinate position calculated by the mobile receiving device 10. It is apparent from the foregoing schematic diagram of the GPS that, when the mobile receiving device 10 does not receive the satellite signal 110 transmitted from the artificial satellites 11, the two or three dimensional coordinate position is not calculated successfully, such that the user cannot obtain the current position. The satellite signals 110 may not be received, for example, in an urban area having crowded skyscrapers or inside a building. That is, when the mobile receiving device 10 is used in an urban having crowded skyscrapers or inside a building, the mobile receiving device 10 may have low utilization efficiency or even be of no use at all.
Therefore, a wireless communication system, such as a Global System for Mobile communications (GSM), a General Packet Radio Service (GPRS) system or a Wideband Code Division Multiple Access (WCDMA), is employed to solve the problem of GPS failures in an urban area having crowded skyscrapers or inside the building. That is, according to the above wireless communication systems, a large number of mobile phone base stations distributed in various areas assist the mobile receiving device to perform positioning. FIG. 2 shows a schematic diagram of positioning a mobile receiving device 20 using a mobile phone base station system 2. When a user using the mobile receiving device 20 such as a mobile phone or a PDA enters an area where satellite signals transmitted from the GPS cannot be received, positioning of the mobile receiving device 20 is taken over by the mobile phone base station system 2 from the GPS. The mobile phone base station system 2 comprises various base station networks A to G in a honeycomb arrangement to cover different areas respectively. A conventional positioning method using the mobile phone base station system 2 is described below. When the mobile receiving device 20 is in an area covered by the base station network A, in addition to receiving a wireless signal of the base station network A, the mobile receiving device 20 simultaneously receives wireless signals of the base station networks B to G. The mobile receiving device 20 transmits strength information of the different wireless signals from the base station networks A to G back to a system server 200 via the mobile phone base station system 2. The system server 200 then calculates current position information of the mobile receiving device 20 according to the strength information of the different wireless signals from the mobile receiving device 20. The system server 200 further transmits the current position information to the mobile receiving device 20, and accordingly the mobile receiving device 20 can perform positioning according to the current position information. Under such structure, the mobile receiving device 20 is enabled to perform positioning in the area having crowded skyscrapers or inside the building where the satellite signals cannot be received.
The technology of using the mobile phone base station system 2 for positioning overcomes the problem of the GPS failures in the urban area having crowded skyscrapers or inside the building. However, it would be desirable if the positioning accuracy were further improved. For example, a positioning accuracy of only about 100 meters is rendered according to the positioning method of using the mobile phone base station system 2. In addition, when the mobile phone base station system 2 is used for positioning, the mobile receiving device 20 at a user end needs to transmit the strength information of the different wireless signals received back to the system server 200, which then transmits the calculated position information back to the mobile receiving device 20 at the user end. However, when the system server 200 at a service provider end does not offer the position information calculation, the mobile receiving device, such as a mobile phone or a PDA at the user end, although having a positioning function, is of no use. Therefore, one main object of the present invention is to overcome the disadvantages incurred when the mobile phone base station system 2 is used for positioning a mobile receiving device.